正支共焦非稳腔的离焦像差特性

Defocus characteristics in positive-branch confocal unstable resonators

正支共焦非稳腔在出光过程中易受环境扰动而造成腔长失调,易受热积累影响而使腔镜变形,从而使输出光束产生离焦像差和部分其它像差。为了实现对离焦像差的校正,针对不同的产生原因,提出了2种离焦像差特性分析方法:一为腔镜相对位置失调引起的离焦像差特性理论分析方法,它是另一种分析方法的基础;二为腔镜变形引起的等效腔长变化导致的离焦像差特性分析方法,它是实际激光器中的主要分析方法。得到了离焦像差与腔长的特性关系和离焦像差与腔镜变形量之间的特性关系。研究表明:腔长改变和腔镜变形对离焦像差的影响本质是一样的,都是改变了谐振腔的共焦点位置;腔长改变或腔镜矢高变化与离焦像差都成近似的线性关系。实验验证了离焦像差特性分析方法的有效性,最后指出离焦像差特性可作为激光器中离焦像差动态补偿的有效依据。

Environmental vibrations may cause the positive-branch confocal unstable cavity length to be maladjusted, moreover, thermal effect directly leads to cavity mirrors distortion. As a result, there will be many kinds of phase aberrations in the output beam. In order to correct the defocus aberration, this paper presents two analytic methods to analyze the defocus aberration generated under two different conditions. One is to analyze the relative position misalignment of cavity mirrors leading to defocus aberrations. The other is to analyze the distortion of cavity mirrors leading to defocus aberrations. The relation of the defocus and cavity length as well as the relation of the defocus and cavity mirrors＇ distortion are obtained. The conclusion results show that the change of the cavity length and the distortion of the cavity mirrors leading to defocus aberrations are the same essentially, that is the same to transform confocal spot position. In addition, the cavity length change quantum and the distortion quantum of cavity mirrors are all linear relationships to the defocus aberration. These two analytic methods are proved to be effective by experiments, and the defocus characteristics have important references for the auto-compensate of the defocus aberration dynamically.